Atomic force microscopy measurements of contact resistance and current-dependent stiction

Abstract

A modified atomic force microscope (AFM) is used to perform contact resistance and/or current-dependent stiction measurements for conductive thin films at controlled values of applied force. The measurements are preferably performed under conditions approximating the operation of the thin films as electrodes in microswitch array fingerprint sensors. A first, planar thin film is contacted with a second, curved thin film deposited over a round ball having a diameter of a few microns to a few tens of microns. The second film is preferably a coating deposited over the ball and over the arm controlling the ball motion. The coating deposited over the arm provides an electrically conductive path to the contact surface of the ball.

1. A method of testing a pair of thin films, each thin film being formed by a material desired for use as a different one of a pair of contact materials, to obtain information that is usable in a determination whether at least one of the pair of contact materials is appropriate for use as a contact material in a switch, comprising:
 performing at least one atomic force microscopy measurement relating to a predetermined characteristic of the pair of contact materials on the pair of thin films after they contact each other with a first controlled force.  
 
     
     
       2. The method according to  claim 1  wherein:
 the predetermined characteristic is a contact resistance; and  
 the step of performing the atomic force microscopy measurement comprises obtaining a contact resistance value between the pair of thin films when the pair of thin films contact each other with the first controlled force.  
 
     
     
       3. The method according to  claim 1  wherein:
 the predetermined characteristic is a current-dependent stiction force; and  
 the step of performing the atomic force microscopy measurement comprises obtaining a stiction force value between the pair of thin films after the pair of thin films contact each other with the first controlled force between the thin films.  
 
     
     
       4. The method according to  claim 1  wherein the predetermined characteristic is resistivity. 
     
     
       5. The method according to  claim 1  wherein the predetermined characteristic is conductivity. 
     
     
       6. The method according to  claim 4 , wherein the step of performing comprises:
 obtaining a resistance value for the pair of thin films when the pair of thin films contact each other due to the first controlled force; and  
 calculating a corresponding resistivity value.  
 
     
     
       7. The method according to  claim 6  further comprising evaluating the resistivity value to determine if the pair of thin films is a conductor appropriate for use in the switch. 
     
     
       8. The method according to  claim 5 , wherein the step of performing comprises:
 obtaining a conductance value for the pair of thin films when the pair of thin films contact each other due to the first controlled force; and  
 calculating a corresponding conductivity value.  
 
     
     
       9. The method according to  claim 8  further comprising evaluating the conductivity value to determine if the pair of thin films is a conductor appropriate for use in the switch.